All I can tell you is to try the rifle. It will decide for you in most cases. Some rifles like a certain powder and can actually hate a different powder. I have a CVA .54 caliber Mountain Stalker.. for the best accuracy I shoot 80 grains of Triple Se7en, a wonder wad or bore button, and a patched roundball. A very effective and accurate rifle with that load. If I load it with pyrodex the group will spread almost another two inches.

Yet I have a Tradition's Hawkins what loaded with Pyrodex RS or Goex 2fand the groups are fantastic.Load it with Triple Se7en and every thing goes down hill from there.

It will really depend on the rifle.

The advantage of Triple Se7en in a traditional is less fowling, and easier to clean. Also you use less powder to gain the same or greater roundball speed. You do have to keep an eye out when shooting TripleSe7en for a hard crud build up in the breech which can hinder the seating of the projectile. A simple damp patch is all that is necessary to correct the matter.

Actually in almost all my traditional rifles I shoot Goex 2f or 3f powder and get excellent results.

__________________"Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, a total wreck, screaming Yahoo, with a big smile on your face."

Triple7 is my current powder of choice, it burns clean, is easy to clean up and is powerfull. Pyrodex, I avoid due to the high corrosive nature of it and it is not much better than black as far as cleanup goes.

Is there any advantage to either in a traditional rifle shooting roundballs?

IMO, Pyrodex is better for PRB shooting. In my experience, I have been unable to find a T7 load that does not blow patches, regardless of patch/ball fit or the amount of powder used. I have never found a T7 load that will shoot consistently with a PRB in .45, .50, or .54 caliber, even when used with a Wonderwad on top of the powder.

The stuff works great for conical bullets with a Wonderwad under them, however.

It is much easier to clean up at the end of the day if you used T7 all day than if you used Pyrodex. But I have never had to wipe between shots to reload when using Pyrodex. Not so with T7, however!

I have never had any luck with 777,pryodex work wel in most guns but is very corrosive, try something modern like APP,Pinnacle or Black Mag.
Go with what works best but I find the lack of crosiveness and crud rings let me enjoy shooting more. Lee